via BigCityMusic – a demo of the Analogue Systems rs510e.

The rs510e is the only licensed version of the Trapezoid Generator from the legendary EMS synths. The rs510e basically has an envelope generator and a VCA built into one module. You can trigger the EG with a gate from a keyboard, sequencer, or the trigger button on the face plate.

The Trapezoid Generator works a lot like a traditional envelope generator but only has three stages. There is Attack, On, and Decay. On a graph, depending on the settings, this forms a trapezoid shape. The rs510e also has an Off knob. Setting this knob fully clockwise results in a more typical EG. Turn it to the left and you have something special. The off knob controls the auto repeat function. The more you turn counterclockwise, the faster it goes. You still have all the other knobs to manipulate as well. Depending on the settings, the rs510e can repeat rather quickly. 

The audio in and outs sport level controls, you can distort the input a bit too. You can also use the rs510e as a modulation source, sending the trapezoid out two different outputs. There’s also a level knob for the trapezoid which allows you to attenuate the output or invert it.